Recently, organic light emitting diodes (OLED) have become a popular and emerging flat-panel display product at home and abroad, because of display characteristics, such as active light emission, a large visibility angle, a short response time, a high luminous efficiency, a wide color gamut, a low operating voltage, a thin panel, capability of fabricating a flexible panel of a large size and a simple fabricating process, and potential of a low cost.
OLED can be divided into passive-matrix OLED (PMOLED) and active-matrix OLED (AMOLED) according to a driving type. An oxide thin film transistor (Thin-Film Transistor, short for TFT) backplane or a low temperature polysilicon TFT is usually used to drive AMOLED. Compared to an amorphous silicon TFT, the oxide TFT backplane has a relatively high mobility, and compared to the low temperature polysilicon TFT, TFT with an ESL structure (etch stop structure) has a simple fabricating process, requires few mask plates, and is easy to achieve a mass production process.
The TFT with the ESL structure has a relatively large parasitic capacitance Cgs, and requires a large storage capacitor Cst enough to ensure a normal display function.